An air conditioning system for performing air conditioning inside an object space has been known. Such an air conditioning system is provided with a CO2 sensor for acquiring a carbon dioxide concentration (hereinafter, referred to as CO2 concentration) in the object space and for introducing outside air such that the CO2 concentration is controlled not to be excessively increased in the object space.
In a case of such a CO2 sensor, a reference value may be deviated due to aging. In consideration of this, the reference value is required to be calibrated or corrected after installing the CO2 sensor. Note that, in a case of the air conditioning system which is installed in general homes or general offices in a building, it is difficult to prepare a test environment. Therefore, in some cases, the calibration is performed based on, as reference, a CO2 concentration in the atmosphere. For example, Patent Literature 1 discloses automatic calibration of the reference value of the CO2 sensor based on the CO2 concentration in the atmosphere. In the configuration of Patent Literature 1, the CO2 concentration of the outside air is assumed to be approximately 400 ppm.
(Patent Literature 1)
Publication of Japanese unexamined patent application No. 2014-115175
However, in the configuration of Patent Literature 1, the calibrated reference value is not necessarily matched with the CO2 concentration in the atmosphere (outside air). Specifically, in Patent Literature 1, an environment, in which a person is resident for 24 hours, is assumed. In the environment where a person exists in the object space, carbon dioxide (CO2) is necessarily emitted. In this case, if an introduction amount of the outside air and an emission amount of CO2 are balanced with each other, it is considered that the CO2 concentration becomes constant. Nevertheless, in the present condition, CO2 is being emitted. For this reason, the reference value, which is calibrated in such a condition, may have an offset, by which the reference value is increased with respect to the CO2 concentration in the atmosphere.